The present invention concerns a carburettor for an internal combustion engine showing a suction port which is in connection with the combustion chamber of the motor and which is fed by liquid fuel via a nozzle and a fuel channel which leads into the suction port. A linearly movable valve needle is arranged to extend into the fuel channel mainly perpendicular to its longitudinal direction and to open or close it. The suction port is possible to throttle down or to close with a throttle which is movable between an open position and a closed position.
Carburettors for internal combustion engines, for example motorcycles, show a suction port which is in connection with the combustion chamber of the motor and which is fed with liquid fuel via a nozzle. The suction port is possible to throttle down and to close with a throttle, which is movable between an open position, and a closed position. The throttle may be cylindrical or of a sheet form and be manoeuvred with the aid of a wire which is in connection with a so called throttle twist grip. The nozzle is usually in connection with a fuel channel which leads into the suction port and is opened and closed with the aid a valve needle which is extending down into the opening of the fuel channel in a direction from the suction port. The valve needle may be rigidly mounted upon the throttle or be in connection with this via a wire. When the suction port is totally open the valve needle or the wire extends across the suction port.
At motorcycles for racing the motors for cycles in the same racing class are to keep certain measures and dimensions. Also the size of the suction port is limited to a maximum diameter. It has been shown that the motor effect could be increased at a given diameter of the suction port if the placement of the valve needle or the corresponding wire across the suction port could be avoided. The American patent publications U.S. Pat. No. 1,793,148 and U.S. Pat. No. 4,123,479 describes carburettors where the suction openings are not influenced by wires or valve needles but they are not suitable for use with among other things motors for motorcycles for racing.
The purpose of the present invention is to achieve a carburettor for an internal combustion engine, which is better than the previously known carburettor constructions. The carburettor according to the invention shows a suction port which is in connection with the combustion chamber of the motor and which is fed with liquid fuel via a nozzle and a fuel channel, which leads into the suction port. A linearly moveable valve needle is arranged to extend into the fuel channel mainly perpendicular to its longitudinal direction and to open and close this. The suction port is possible to throttle down or to close with a throttle, which is situated on the opposite side of the suction port in relation to the fuel channel orifice, which is moveable between an open position and a closed position. The valve needle is in connection with a manoeuvre arm which is arranged on one side of the suction port and which in turn is in connection with the throttle and is arranged to open the fuel channel when the throttle is opened and to close the same when the throttle is closed.
In a preferred mode of execution of the invention the manoeuvre arm is turnable arranged towards an axis, its one end being in connection with the outer end of the valve needle and its other end being in connection with a wedge formed part arranged upon the throttle.
In a first alternative mode of execution of the invention the axial position of the valve needle in relation to the manoeuvre arm is setable with the aid of an open spring washer, a so called xe2x80x9cknasterxe2x80x9d, which is possible to place in an optional groove in the valve needle and which allows the manoeuvre arm may be fastened in different positions along the length of the valve needle.
In a second alternative mode of execution of the invention the manoeuvre arm may be divided into two parts, whereby a first part abuts the throttle and the second part is in connection with the valve needle and whereby the mutual position of the parts is setable with the aid of a set screw.
In further alternative modes of execution of the invention the manoeuvre arm may be formed like a wedge at that end which is in contact with the valve needle and connected with the throttle so it moves linearly at the movement of the throttle and closes the fuel channel when the throttle is closed.
It is also within the framework of the invention to design the fuel channel in the form of a pipe which extends out a bit into the suction port or to let the nozzle constitute a part of the fuel channel.
Further details and characteristics regarding the invention are evident from the description of the figures below as well as from the patent claims.